Mechanical Digestion
Mechanical digestion is carried out throughchewing,swallowingand movements that occur in the digestive tract, calledperistaltic movementsorperistalsis.
Chewing and Swallowing
During digestion, in its mechanical process, food is chewed and reduced to very small pieces, with the help of the teeth and tongue. The contact of food with saliva facilitates its passage through the digestive tract.
After chewing and salivation, thefood bolusis formed and swallowed. During swallowing, thesoft palateis retracted upwards and thetonguepushes the food backwards, throwing it into thepharynx, which contracts and projects the food bolus into theesophagus.
When we swallow, theepiglottiscloses the glottis, preventing food from going into the trachea .
Esophagus
The esophagus is a muscular duct that carries out involuntary contractions calledperistaltic movementsorperistalsis, which carry the food bolus to the stomach , where the chemical process of digestion begins.
Chemical Digestion
Inchemical digestion, food is broken down into smaller particles thanks to the action ofenzymespresent in the digestive juice, undergoing changes in its chemical composition.
Stomach
In thestomach,peristaltic movements mix the food bolus with gastric juice, produced by the glands of the gastric mucosa. This juice containshydrochloric acid, which maintains stomach acidity, providing favorable conditions for the work of enzymes in digestion.
Pepsin , the main enzyme in the stomach, acts to transform proteins, intensifying chemical digestion. The hormone gastrin (produced in the stomach when food comes into contact with its walls) regulates the action of pepsin, which transforms large molecules (polypeptides) into smaller molecules (dipeptides).
The food juice resulting from chemical digestion is calledchyme. The passage of chyme into the intestine is controlled by a valve calledthe pylorus.
Small intestine
Most of the digestion and assimilation of nutrients takes place in thesmall intestine. Two regions can be distinguished: the duodenum and the jejunum-ileum.
Secretions from the liver and pancreas are released into theduodenum, which, together with enteric or intestinal juice, act on the chyme (a bolus of food that looks like a white mass after passing through gastric digestion).
- Bile:is the secretion ofthe liver,stored in thegallbladder, which is released into the duodenum through the common bile duct.Biledoes not contain digestive enzymes, but ratherbile salts(mainly water and sodium bicarbonate) that separate fats into microscopic particles, facilitating the action of pancreatic enzymes on lipids .
- Pancreatic juice:produced by the pancreas.Trypsinis one of the enzymes produced in the pancreas, which acts on proteins. It only becomes active when it reaches the duodenum and joins the enteric juice, transforming intochymotrypsin.
- Intestinal or enteric juice:is produced by the intestinal mucosa. It contains enzymes that complete the digestion of lipids, proteins and carbohydrates .
At the end of the process carried out in the duodenum, the set of substances forms a viscous white liquid, calledchyle, which goes to the jejunum-ileum.
In thejejunum-ileum,a large part of the nutrients resulting from the digestion process are absorbed by the blood and carried to all the cells of the body. What is not absorbed – water and food mass, mainly made up of fiber – passes to the large intestine.
Dietary fiberis therefore essential for the formation of feces and the proper functioning of the intestines.
Large intestine
The large intestine absorbs water and mineral salts that the small intestine did not assimilate during digestion. The undigested material forms feces, which accumulate in therectum(the final part of the large intestine) and are subsequently pushed out through peristaltic movements through theanus.